Enforcing honesty in fair exchange protocols

Abstract

When buying and selling digital products online both the customer and merchant need to trust each other. However, not all parties are honest and hence a class of exchange protocols has been developed that are called Optimistic Fair Exchange Protocols. This paper surveys the field of Fair Exchange Protocols and then presents a special type of protocol between a customer (C) and a merchant (M) that enforces one of them to be honest. It makes minimal use of a Trusted Third Party (TTP). The protocol has the features that it: (1) only comprises three messages to be exchanged between C and M; (2) guarantees strong fairness for both C and M; (3) allows both parties to be sure of the item that they will receive from the other party; and (4) resolves disputes automatically online.